Changing and removing values from deeply nested QVariant - qt

Question

I'm using QVariant to manage the project settings of our In-House application.
For this I'm using a nested QVariantMap recursively containing QVariantMaps and leaves holding the actual values.
Now, I found it quite cumbersome to set and remove nodes from this tree like structure. Especially, if the nesting reaches a certain depth.
Part of the problem is, that value<T> returns a copy instead of a reference. (I'm wondering, why Qt is lacking this feature??)
#include <QVariantMap>
#include <QDebug>
int main(int argc, char** args) {
QVariantMap map = { {"A", QVariantMap{ {"B",5.} }} };
{
// Change value
auto nested = map["A"].value<QVariantMap>();
nested["B"] = 6;
map["A"] = nested;
qDebug() << map;
// What it should be
// map["A"]["B"] = 5;
}
{
// Remove value
auto nested = map["A"].value<QVariantMap>();
nested.remove("B");
map["A"] = nested;
qDebug() << map;
// What it should be
// map["A"].remove("B");
}
}
What might be the easiest way to directly set and remove values and to make my function a one-liner? Performance is not critical, but ease of usability is definitely an issue for me.

Answer 1

After some thought I came up to the idea to use a path to my desired value. This path should be unique.
The following code recursively finds the value and removes it. Changing a value should be quite similar. I'm not sure, if there might an easier approach.
bool remove(QVariantMap& map, const QString& path, QString sep = ".") {
auto elems = path.split(sep);
if (elems.size() > 1) {
if (!map.contains(elems.first())) return false;
auto tmp = elems;
tmp.pop_front();
auto childMap = map[elems.first()].value<QVariantMap>();
bool ret = remove(childMap, tmp.join("."));
if (!ret) return false;
map[elems.first()] = childMap;
return true;
}
else if (elems.size() == 1) {
return map.remove(elems[0]) >= 1;
}
else {
return false;
}
}
Remark
This solution should not be used, if there is a lot of data, as there is quite a lot of copying of maps.